1. Field of the Invention
The present invention relates to a method of producing an optical waveguide and more particularly to a method of producing a polarization-maintaining single-mode optical waveguide and a preform used therein.
2. Description of the Prior Art
A method for producing such a waveguide is disclosed in European patent application No. 0 145 031. In this known method, a preform is provided wherein the ratios between the inside diameter of a tube of cladding material, the outside diameter of a rod centrally disposed therein, and the diameters of four rods arranged in between are so chosen that a large interstice remains between one rod and the next rod located in the circumferential direction of the inside circumference of the tube. Rods of cladding material are fitted into these interstices.